My Machine did the same. It turned out to be a small piece of black plastic that sits near the electrical impulse command. A sewing machine chap fixed it for me. The original piece had broken off and I found it later sitting under the machine. Just as well I don't dust too often! Another machine the same happened to come in the same week and he was able to make a replacement piece prior to me finding the original. Before I found him I had taken it to everywhere and was told that it was unfixable.Hope this helps.
Maxine
June 2014